In the sea-anemone affixing itself to the shell of the hermit-crab, who becomes its friendly and interested landlord, we have seen one of the more pleasing instances of association between two or more different species of animals. There are many others, such as that between the shark and the pilot-fish, the honey-guide and the ratel, the rhinoceros and its little bird, etc., etc., which we can dwell upon with equal pleasure. Some, however—and, unfortunately, they are much more numerous—are of a darker character, repelling us almost as much by the picture which they present of nature’s unbending cruelty as they arouse our admiration by their wonderful ingenuity and adaptation of means to ends. The most salient examples of this kind of living together—partnership we can hardly call it—are to be found, perhaps, in the insect world. Parasitism is the proper word for it, and the most salient, or at least the most repulsive, examples are furnished perhaps by the hymenoptera—that genus of insects in which the bees, wasps, and ants are included. Thus almost all caterpillars—perhaps all—are victimised by some species of ichneumon-fly—a wasp-like creature that seeks it out, pierces its soft body with a long ovipositor, with which it is provided for the purpose, and lays a number of eggs inside it. Having done this, it goes away, and the caterpillar goes on feeding. It is, however, doomed, and destined never to enter into the moth or butterfly state of existence. In due time the eggs are hatched by the warmth of its own body, and on this body to which they are so highly indebted, the young ichneumons, now in their own caterpillar state, begin with unconscious ingratitude to prey. They feast upon it day and night, but the creature, ordained by the iron laws of nature to suffer in this way, is long-lived, and though sickening from day to day, has often sufficient strength to become full-fed, and make its cocoon, and pass into the chrysalis, or pupal, state. How long it lives after that it is difficult to say. Probably some vitality remains as long, or almost as long, as any part of itself does. All that we know is that after a longer or shorter interval a score or so of ugly, evil-looking ichneumon-flies issue from the dry shell of the chrysalis, instead of the innocent and radiant creature that would otherwise have done so.